The present invention relates to a method of forming silicon nitride on a substrate.
Silicon nitride (Si3N4) is a commonly used dielectric material in semiconductor and integrated circuit (IC) fabrication. For example, a silicon nitride layer may be used to prevent moisture and contaminants from entering an IC package, or to prevent mechanical and chemical damage during assembly and packaging of the integrated circuit. In such applications, the silicon nitride is deposited over the entire top surface of a substrate to serve as a passivation layer.
Silicon nitride is also used in certain integrated circuits for special applications. For example, the E2PROM and Flash memory type integrated circuits use a NO structure to serve as a dielectric layer between floating and control gates. Such applications utilize the high dielectric constant of Si3N4. Silicon nitride is also used to isolate circuit devices in integrated circuits having tens of thousands of semiconductor devices to allow increased integrated circuit density. The circuit devices are initially formed in the silicon substrate and thereafter electrically isolated with silicon nitride material to ensure proper operation of the devices. Si3N4 may also be used as a gate spacer because of its good dielectric constant properties.
Typically, silicon nitride is deposited on the substrate by a low pressure chemical vapor deposition (LPCVD) process. In the LPCVD method, a nitrogen-containing gas, such as ammonia (NH3), is reacted in the vapor phase with a silicon-containing gas, such as SiH2Cl2 or SiH4, to deposit a layer of silicon-nitride on the substrate. For example, when SiH2Cl2and NH3 gas are used as the reaction gases in an LPCVD process, it is believed that the chemical reaction is as follows: 
However, such conventional silicon deposition methods often result in the deposition of a silicon nitride layer having a non-uniform and variable thickness. These thickness variations may result from differences in the rate of dissociation of the ammonia, SiH2Cl2 or SiH4 gas, and the loading effect that arises at the sidewalls of trenches in which the silicon nitride is deposited. Thus, it is often difficult to control the thickness uniformity of the deposited silicon nitride film in conventional LPCVD methods, and it is desirable to have a process for depositing silicon nitride material on a substrate with better uniformity and less thickness variability.
A method of forming silicon nitride material on a substrate, comprises providing a substrate in a reaction chamber, introducing a nitrogen-containing gas into the reaction chamber so that a portion of the nitrogen-containing gas is chemically adsorbed on the substrate surface, pumping down the reaction chamber to remove the nitrogen-containing gas, and introducing a silicon-containing gas into the reaction chamber, wherein the silicon-containing gas reacts with the adsorbed nitrogen-containing gas to form silicon nitride on the substrate.
In another method of forming silicon nitride material, a substrate is provided in a reaction chamber. In a first stage, a nitrogen-containing gas is flowed into the reaction chamber, the flow of the nitrogen-containing gas is stopped, and the reaction chamber is pumped down to remove the nitrogen-containing gas. In a second stage, a silicon-containing gas is flowed into the reaction chamber, the flow of the silicon-containing gas is stopped, and the reaction chamber is pumped down to remove the silicon-containing gas.